Camille Thomas
@camthomas.bsky.social
He/him, Geomicrobiologist @ Uni. Bern, wannabe psycho-historian of rocks and life. Team player, father, ally. Co-founder of @sedimentologika.bsky.social
We are at the #IPA-IAL meeting in Aix les Bains, to hear about the latest on lake research. The room is already crowded at the #sedaDNA session @ialipa2025.bsky.social
October 6, 2025 at 9:32 AM
We are at the #IPA-IAL meeting in Aix les Bains, to hear about the latest on lake research. The room is already crowded at the #sedaDNA session @ialipa2025.bsky.social
Also lake Bourget is truly beautiful !
February 27, 2025 at 8:46 AM
Also lake Bourget is truly beautiful !
@sedimentologika.bsky.social is now part of the Free Journal Network, and we are super proud of it! 🔥
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November 21, 2024 at 10:24 AM
@sedimentologika.bsky.social is now part of the Free Journal Network, and we are super proud of it! 🔥
sedimentologika.org
freejournals.org
sedimentologika.org
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time to take off for our scientific drilling in Tibet! DNA sampling in lake Nam Co sediments coming up
May 30, 2024 at 1:15 AM
time to take off for our scientific drilling in Tibet! DNA sampling in lake Nam Co sediments coming up
As a conclusion, while we do not question here the interpretations of fossil stromatolites, our Dead Sea example presents an extreme case where intense arsenic concentrations can be potentially recorded in a fossil record as a result of arsenic detoxification, and not arsenotrophy. 29/n
March 6, 2024 at 10:39 AM
As a conclusion, while we do not question here the interpretations of fossil stromatolites, our Dead Sea example presents an extreme case where intense arsenic concentrations can be potentially recorded in a fossil record as a result of arsenic detoxification, and not arsenotrophy. 29/n
Such organic-matter and arsenic-rich lamina were found in Archean stromatolites, like the 2.7Ga Tumbiana Formation, Australia. They were interpreted to bear some of the first occurrences of anaerobic methane oxidation, nitrification, denitrification & arsenotrophy (Sforna et al., 2014) 28/n
March 6, 2024 at 10:37 AM
Such organic-matter and arsenic-rich lamina were found in Archean stromatolites, like the 2.7Ga Tumbiana Formation, Australia. They were interpreted to bear some of the first occurrences of anaerobic methane oxidation, nitrification, denitrification & arsenotrophy (Sforna et al., 2014) 28/n
This was likely a rare event, that could not be measured in the water when we sampled it, but which can be recorded in microbial mats. If time and conditions allow, it can then be potentially preserved in an organic lamina when the microbes build up a stromatolite. 27/
March 6, 2024 at 10:30 AM
This was likely a rare event, that could not be measured in the water when we sampled it, but which can be recorded in microbial mats. If time and conditions allow, it can then be potentially preserved in an organic lamina when the microbes build up a stromatolite. 27/
so here we suspect that at some point, a large pulse of arsenic was naturally (?) released in our sinkhole, triggering a protection and detoxification reaction by the microbial mat, that worked hardly to store arsenic into non-toxic organoarsenics, away from the cells, in their EPS. 26/n
March 6, 2024 at 10:25 AM
so here we suspect that at some point, a large pulse of arsenic was naturally (?) released in our sinkhole, triggering a protection and detoxification reaction by the microbial mat, that worked hardly to store arsenic into non-toxic organoarsenics, away from the cells, in their EPS. 26/n
We are not so sure about this. For the 1st time, arsenic is detected to this levels around the Dead Sea, but pulses arsenic are not uncommon in groundwater systems, especially dynamic ones. The Dead Sea sinkholes migration patterns by Abelson et al. (2017) shows how dynamic it can get. 25/n
March 6, 2024 at 10:19 AM
We are not so sure about this. For the 1st time, arsenic is detected to this levels around the Dead Sea, but pulses arsenic are not uncommon in groundwater systems, especially dynamic ones. The Dead Sea sinkholes migration patterns by Abelson et al. (2017) shows how dynamic it can get. 25/n
This is a quite common phenomenon. Most living cells can perform this operation. So this is not a very sexy result. But it suggests that this mechanism can permit to accumulate arsenic to very high levels in microbial mats of the environment. But why? 24/n
March 6, 2024 at 9:59 AM
This is a quite common phenomenon. Most living cells can perform this operation. So this is not a very sexy result. But it suggests that this mechanism can permit to accumulate arsenic to very high levels in microbial mats of the environment. But why? 24/n
These results show that microbes living in the mat can get rid of poisonous material by transforming arsenic contaminants into less mobile and toxic organoarsenic molecules we found today accumulated in the Dead Sea mat. 23/n
March 6, 2024 at 9:58 AM
These results show that microbes living in the mat can get rid of poisonous material by transforming arsenic contaminants into less mobile and toxic organoarsenic molecules we found today accumulated in the Dead Sea mat. 23/n
By looking at this mat under epifluorescent microscope, we indeed noticed that where arsenic could be mapped, organic matter was prevailing, under the form of exopolymeric substance produced by diverse communities, including filamentous cyanobacteria.
March 6, 2024 at 9:52 AM
By looking at this mat under epifluorescent microscope, we indeed noticed that where arsenic could be mapped, organic matter was prevailing, under the form of exopolymeric substance produced by diverse communities, including filamentous cyanobacteria.
This tells us that arsenic is not in its most dangerous form, and that most of the mat had a similar composition in terms of arsenic. Also, arsenic has been bond to organic matter by a specific process, yet to be evidenced. 19/n
March 6, 2024 at 9:49 AM
This tells us that arsenic is not in its most dangerous form, and that most of the mat had a similar composition in terms of arsenic. Also, arsenic has been bond to organic matter by a specific process, yet to be evidenced. 19/n
In collaboration with Montserrat Filella from Univ. Geneva and Dario Ferreira Sanchez at the Paul Scherrer Institute, we interpreted most of the arsenic to be linked with organic elements, under the form of oxidized arsenic. 18/n
March 6, 2024 at 9:46 AM
In collaboration with Montserrat Filella from Univ. Geneva and Dario Ferreira Sanchez at the Paul Scherrer Institute, we interpreted most of the arsenic to be linked with organic elements, under the form of oxidized arsenic. 18/n
Arsenic is a Group 1 human carcinogen, contaminating food and ground water. So knowing how it has been mobilized and immobilized in nature is very important. So we tried to investigate under what form it was in the mat by going to the Swiss Light Source Synchrotron. 17/n
March 6, 2024 at 9:44 AM
Arsenic is a Group 1 human carcinogen, contaminating food and ground water. So knowing how it has been mobilized and immobilized in nature is very important. So we tried to investigate under what form it was in the mat by going to the Swiss Light Source Synchrotron. 17/n
We mapped arsenic more closely in the mat, using XRF and particle-induced X-ray emissions, allowing quantification of numerous elements at high resolution. Arsenic was tied to other elements like Mg, Si, and Mn. This was in collaboration with AIFIRA member Stephanie Sorieul.
14/n
14/n
March 5, 2024 at 4:47 PM
We mapped arsenic more closely in the mat, using XRF and particle-induced X-ray emissions, allowing quantification of numerous elements at high resolution. Arsenic was tied to other elements like Mg, Si, and Mn. This was in collaboration with AIFIRA member Stephanie Sorieul.
14/n
14/n
So we went a little bit further to try to understand what was the nature of this arsenic enrichment. I created a poster explaining the step by step process for a congress. I will detail it below.
13/n
13/n
March 5, 2024 at 4:44 PM
So we went a little bit further to try to understand what was the nature of this arsenic enrichment. I created a poster explaining the step by step process for a congress. I will detail it below.
13/n
13/n
Covid lock down started. Our microbial communities, although adapted to life in extreme environments could hardly be monitored & and we were missing many supplies. So abandoned part of the project, and redirected to analyses, easier to postpone or delay. Life found its way though
10/n
10/n
March 5, 2024 at 4:35 PM
Covid lock down started. Our microbial communities, although adapted to life in extreme environments could hardly be monitored & and we were missing many supplies. So abandoned part of the project, and redirected to analyses, easier to postpone or delay. Life found its way though
10/n
10/n
We eventually sampled many of them, for their DNA, chemistry, microscopic investigation and laboratory growth. Then went back to our lab in Switzerland at the University of Geneva, and prepared for the next steps. That was January 2020.
9/n
9/n
March 5, 2024 at 4:33 PM
We eventually sampled many of them, for their DNA, chemistry, microscopic investigation and laboratory growth. Then went back to our lab in Switzerland at the University of Geneva, and prepared for the next steps. That was January 2020.
9/n
9/n
One pool caught our attention as it had a well laminated and mineralized microbial mat looking like some of the oldest stromatolites recovered from Australia for example.
8/n
8/n
March 5, 2024 at 4:28 PM
One pool caught our attention as it had a well laminated and mineralized microbial mat looking like some of the oldest stromatolites recovered from Australia for example.
8/n
8/n
As we visited these sinkholes in the Dead Sea, with D. Ariztegui, A. Agnon and N. Gedulter, we found some of these ecosystems with different t° or salinity, which lead to changes in how the microbes looked like. Some were purple, some green, some aggregated and formed minerals, others did not 7/
March 5, 2024 at 4:27 PM
As we visited these sinkholes in the Dead Sea, with D. Ariztegui, A. Agnon and N. Gedulter, we found some of these ecosystems with different t° or salinity, which lead to changes in how the microbes looked like. Some were purple, some green, some aggregated and formed minerals, others did not 7/
These sinkholes form along the Dead Sea shores and follow the lake retreat mainly caused by human activity pumping water for agriculture and to extract minerals in giant evaporative pans. 10 years ago, the Dead Sea Works company was the 4th largest potash production company in the world. 4/n
March 5, 2024 at 4:20 PM
These sinkholes form along the Dead Sea shores and follow the lake retreat mainly caused by human activity pumping water for agriculture and to extract minerals in giant evaporative pans. 10 years ago, the Dead Sea Works company was the 4th largest potash production company in the world. 4/n
Varied colors are formed by microbial communities developing in pools/sinkholes thanks to the dilution of Dead Sea brine. Salinity is much lower there than in the lake, where no photosynthetic activity can be sustained. Mixed minerals also influence the color (Dead Sea kidney by Tzvika Stein). 3/n
March 5, 2024 at 4:18 PM
Varied colors are formed by microbial communities developing in pools/sinkholes thanks to the dilution of Dead Sea brine. Salinity is much lower there than in the lake, where no photosynthetic activity can be sustained. Mixed minerals also influence the color (Dead Sea kidney by Tzvika Stein). 3/n
It started with fieldwork by the Dead Sea shores, where sinkholes are being formed by the circulation of fresher water into the evaporitic subsurface. The lake retreats by ca. 1m per year, leaving halite and gypsum that can be readily dissolved. A lot of springs emerge in those systems
2/n
2/n
March 5, 2024 at 4:15 PM
It started with fieldwork by the Dead Sea shores, where sinkholes are being formed by the circulation of fresher water into the evaporitic subsurface. The lake retreats by ca. 1m per year, leaving halite and gypsum that can be readily dissolved. A lot of springs emerge in those systems
2/n
2/n
